1. Field of the Invention
The present invention relates to a hydrostatic transmission suitable for various industrial vehicles.
2. Related Art
Hydrostatic transmissions are generally well known. For example, Japanese Utility Model Publication Gazette No. Hei 4-50180 discloses a hydrostatic transmission for an industrial vehicle that vertically disposes the hydraulic pump and hydraulic motor so that the input shaft which is engageable with the hydraulic pump is extended to be utilized as a PTO shaft. This arrangement permits the hydrostatic transmission to drive pumps or accessories in addition to the drive system of the industrial vehicle. When a clutch must be provided for selectively connecting and disconnecting the power of a PTO shaft, the clutch must be disposed outside of the housing because of the lack of required space therein. Therefore, lubrication and/or maintenance of the clutch must be separately carried out, and the transmission as a whole becomes larger.
Similarly, Japanese Utility Model Laid-Open Gazette No. Sho 63-27758 discloses a transaxle, including the axles of drive wheels, for an industrial vehicle to which the hydrostatic transmission of the aforesaid type is attached. In this configuration, the transaxle is equipped with a PTO shaft and is provided with hydraulic operation clutch means for selectively connecting and disconnecting the transaxle from the hydrostatic transmission. The transaxle also includes a stepped gear transmission for changing the torque ratio between an input shaft of the hydrostatic transmission and the wheel axles. Because the clutch means is provided in the axle casing, various sizes of transaxles must be prepared according to the specifications of the target industrial vehicles. This is because the transaxle must also be provided with hydraulic equipment such as a control valve for switching the clutch means. Finally, when the clutch means is a hydraulic operation type, a separate hydraulic power source must also be provided.
Therefore, what is needed is a hydrostatic transmission flexible enough to accommodate a variety of industrial needs, yet without the aforesaid disadvantages.